Systems for detecting the presence of a radar signal, for example, a signal emitted by a police radar gun toward a traveling car, are generally known. Thus, for example, U.S. Pat. No. 5,010,341 discloses a passive radar detector that includes a comparator, a pulse stretcher, and a ripple counter. An alarm signal is generated when the number of pulses counted exceeds a predetermined value. U.S. Patent No. 5,083,129 discloses a radar detector that includes front and rear antennae. The signal strength from the antennae is compared to determine direction of origin of the radar signal. U.S. Pat. No. 5,001,777 discloses a radar detector that includes front and rear receivers connected to a single control head. A signal strength indicator varies proportionally to the intensity and frequency of the signal.
As radar guns have evolved, so have radar detectors. Thus, current state of the art radar guns emit pulsed laser signals in the infrared frequency range. Such guns have created a new set of signal processing problems related to higher frequency signals, and there is presently no adequate solution for detecting and indicating the presence of a laser-based signal. In this regard, applicant is aware of U.S. patent application Ser. No. 407,568, filed Sep. 15, 1989, although applicant does not admit that this application or the invention described therein is prior art relative to the present invention. The claims of this application recite a hand-held laser detector that converts the optical laser pulse to a first electrical signal, then passes the first signal through a threshold gate only if the first signal exceeds a predefined signal strength. A second signal is generated if the pulse width of the first signal is less than a predefined pulse width value, and this condition is indicated by an indicator means. A delay circuit prevents the second signal from being cancelled if a laser pulse having a pulse width greater than the predefined pulse width value is received shortly after the second signal has been generated.
U.S. Pat. No. 4,277,170 discloses an aircraft collision avoidance system that includes a laser detector. The detector includes a discriminator circuit, including a threshold network and a delay network, for passing only those signals which have time behavior similar to the anticipated laser signal.
Thus, it would be desirable to have a system that reliably and accurately detects the presence of a pulsed-laser signal and provides and indication of the same, including an indication of the relative threat of the signal.